The Canadian Mineralogist; June 2007; v. 45; no. 3;
p. 479-483; DOI: 10.2113/gscanmin.45.3.479
© 2007 Mineralogical Association of Canada
KOCHSÁNDORITE, A NEW Ca–Al CARBONATE MINERAL SPECIES FROM THE MÁNY COAL DEPOSIT, HUNGARY
István E. Sajó1,
and
Sándor Szakáll2
1 Chemical Research Center of the Hungarian Academy of Sciences, Pusztaszeri út 59–67, H–1025 Budapest, Hungary
2 Department of Mineralogy and Petrology, University of Miskolc, H-3515 Miskolc, Egyetemváros, Hungary
E-mail address: sajo{at}chemres.hu
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ABSTRACT
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Kochsándorite, ideally CaAl2(CO3)2(OH)4·H2O, is a newly identified mineral species from the Mány coal deposit, north-western Hungary. The mineral occurs as spherical aggregates of colorless acicular crystals up to 0.5 mm long, forming white to pale brown strings in the massive coal. The streak is white, and the crystals have a vitreous to silky luster. The forms, in order of prominence, are: {100}, {110}, {001} and {010}. No cleavage is evident. The mineral is brittle, and its Mohs hardness is about 2–2.5. Optically, the mineral is biaxial (–), 
1.597(3), ß not determined, 
1.603(6). No pleochroism was observed. Associated minerals at the type locality are quartz, pyrite, böhmite, dolomite, calcite, gibbsite, kaolinite, illite, alumohydrocalcite, gypsum and felsöbányaite. The mineral is orthorhombic, space group Pnma, with the following unit-cell parameters, refined from powder data: a 15.564(6), b 5.591(4), c 9.112(4) Å, V 792.9(3) Å3. With Z = 4, the calculated density is 2.514(2) g/cm3, and the measured density is 2.486(20) g/cm3. The mineral dissolves quickly in dilute HCl with effervescence.
Keywords: kochsándorite, new mineral species, carbonate of Ca and Al, Mány coal deposit, Hungary.
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INTRODUCTION
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Nodules one to two cm across were found about a hundred years ago in the Eocene coal deposits of the Tatabánya coalfield, in the northeastern part of the Transdanubian Mountains, Hungary. These nodules were called huszárzsinór or "hussar string" by the coal miners, alluding to the characteristic decorations of the hussars’ uniform. Two or three parallel strings usually are developed together. The nodules are massive and earthy or exhibit a radiating texture. They are accompanied by macroscopic nodules and impregnations of pyrite. The "hussar string" samples were first studied by Vadász (1941). He observed that the nodules occur in orderly lines at the lower levels of the Tatabánya coal deposit. From the analytical data on bulk samples obtained by wet-chemical methods, the main constituents of the nodules were determined to be gibbsite, alumohydrocalcite, and pyrite. Their formation was linked to the formation of pyrite from the hydrogen sulfide of sapropel origin in an acidic, oxygen-poor environment. Szádeczky-Kardoss (1952) discussed the genetic aspects of the mineral assemblage of a "hussar string". He proposed that it forms in an alkaline environment, which had become alkaline as a result of the surrounding karstic formations. Csajághy & Zamaróczy (1959) described the "hussar string" from other shafts and gave a detailed review of the occurrence of these mineral precipitates in the Tatabánya coalfield, together with further analytical data. They noted that a sample similar to those earlier described as alumohydrocalcite now proved to be the mixture of böhmite and calcite. In the second half of the 20th century, owing to intensive coal mining, it turned out that the "hussar string" occurrences are widespread in the lower part of some coal deposits.
The new mineral species is named after Sándor Koch (1896–1983), formerly professor in the Department of Mineralogy, Petrography and Geochemistry, József Attila University (now University of Szeged). He was a prominent figure in the research on Hungarian mineralogy in the 20th century, especially in topographic and descriptive mineralogy. His principal work is the Minerals of Hungary(1966); he was the coauthor of the descriptions of fülöppite and mátraite.
Both the mineral and mineral name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association (#2004–037). The mineral is preserved in the mineral collection of the Hungarian Natural History Museum, Budapest (catalog number 568/2004), Herman Ottó Museum, Miskolc (catalog number 2004.72) and Minerals of the Carpathian Basin – Mineral Museum of Lajos Kövecses-Varga, Siófok (catalog number 12004/1–3).
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OCCURRENCE
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The locality of the new mineral is the I/A shaft (47°32' N, 18°40' E) of the coal mine in Mány. The mine is situated 15 km east of the Tatabánya coal mine. Both coal deposits are of Eocene age. Underlying the layers of coal is Triassic dolomite. Between the dolomite and the coal beds, there is a significant amount of dolomitic breccias, which contain bodies of bauxite. In the coal-rich series, three coal beds were identified. Travertine and marl layers occur between the lower and middle beds (Gerber 1978). The "hussar strings" mainly occur in the lower beds. Characteristically, they appear in oval, earthy or massive nodules, 1–2 cm in diameter. In some cases, there are secondary precipitations as encrustations 1–4 mm in thickness, parallel to the coal beds (Fig. 1a). Primary minerals syngenetically formed within the coal beds are pyrite, böhmite, and calcite. Secondary minerals are gibbsite, gypsum, kochsándorite, poorly crystalline Fe-oxides and, in a lesser amount, kaolinite, illite, alumohydrocalcite and felsöbányaite. The new species was formed by the contemporaneous weathering of böhmite, pyrite and calcite. Radial aggregates of the new mineral formed at the expense of intensely weathered nodules of böhmite are commonly observed (Fig. 1b). Kochsándorite was also identified recently in samples collected from the Tatabánya coal mine in the middle of the last century. The appearance is similar to that at the type locality, where kochsándorite is found in white veins in coal, usually intimately intergrown with gibbsite, most commonly associated with calcite and gypsum.
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FIG. 1. Brown coal from Mány, containing a layer of kochsándorite spherules (field of view 22 mm wide), (b) Böhmite (bhm) nodules and kochsándorite (ko) replacing böhmite (field of view 40 mm wide).
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PHYSICAL AND OPTICAL PROPERTIES
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The kochsándorite crystals are acicular, and form radial aggregates on the wall of fissures or in cavities within oval nodules in brown coal (Fig. 2). In the aggregates, the length of the bladed to needle-like crystals is typically 200–300 µm, the width is 2–10 µm (Fig. 3). The forms identified by SEM are: {001}, {010}, {100}, {110}. The dominant forms are {100} and {110}. Twinning was not observed. Kochsándorite is white to colorless. It has a vitreous to silky luster (the latter only in the case of aggregates). The streak is white. It produces a pale yellow color in UV light of both short and long wavelength. The Mohs hardness was not accurately determined, but it is estimated to be about 2 or 2
. The crystals are quite brittle. A definite cleavage or characteristic fracture was not observed. Kochsándorite is not soluble in water. It is easily soluble in dilute hydrochloric acid, with a moderate effervescence. The density measured using the sink–float technique (with a pycnometer, in an acetone–bromoform mixture) is 2.486(20) g/cm3. The calculated density is: 2.514 (2) g/cm3. The crystals are biaxial negative. The indices of refraction in 546 nm light are 1.597(3), ß not determined, 1.603(6). The 2V could not be measured. The dispersion r < v is weak. Pleochroism was not detected.
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CHEMICAL COMPOSITION
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The chemical composition of kochsándorite was determined using prompt gamma activation analysis (PGAA), energy-dispersive X-ray spectrometry (EDS) and thermogravimetry (TG–MS).
The PGAA measurements were carried out in the PGGA facility using the cold neutron beams at the Budapest Research Reactor (Révay et al. 2004). The technique is most useful for measurement of levels of the light elements such as H, B, C, N, Si, P, S, Cl (Révay & Belgya 2004). Furthermore, the sensitivity of the measurements enables us to prove the absence of substituents at Ca2+ and Al3+ positions. Barium, Sr, Pb and Cr concentrations in each sample are well below 1000 ppm each. Minor amounts of the rare-earth elements (REE) are detected: 34 ppm Sm, 50 ppm Eu, 40 ppm Gd and 600 ppm Dy.
EDS analyses were done in an AMRAY 1830 I electron microprobe fitted with an EDAX DX–4 solid-state detector, with a beam diameter of 2 µm, an operating voltage of 25 kV, and a beam current of 5 x 10–11 A. The raw data were corrected with the kZAF program.
A thermal analysis was done using a Perkin–Elmer TGS–2 thermobalance equipped with HIDEN HAL 2/301 PIC quadrupole mass spectrometer. The instrument was calibrated with calcium oxalate as a reference standard. The TG/MS measurements were done on pure samples up to 1000°C. The DTG curve exhibits two peaks, a stronger one at 350°C and a weaker one at 930°C. The first DTG peak is associated with the combined loss of all H2O and more than half of CO2. The 930°C peak results from the loss of remaining CO2, as determined by mass spectrometry (MS).
The empirical formula based on Al = 2 atoms per formula unit, assuming charge neutrality is: Ca0.9 Al2(CO3)1.9(OH)4·1.3H2O. The simplified formula is CaAl2(CO3)2(OH)4·H2O, in analogy with the isostructural minerals of the dundasite – dresserite group. The exact H2O content of these minerals is still not determined with certainty (Jambor et al. 1977, Birch et al. 2000). For kochsándorite, the 1000°C loss on ignition (LOI) value (47.3%) is in remarkably good agreement with that calculated from the above simplified formula (47.34%). The 1000°C residue of the TG-measured sample consists of pure CaAl2O4 (as determined by XRD), corroborating the 1:2 Ca:Al stoichiometry in the formula of the mineral.
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INFRARED SPECTROSCOPY
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Infrared spectra in the 4000–400 cm–1 range were recorded on a Thermo Nicolet Avatar 320 FT–IR spectrometer using KBr discs. The FTIR spectrum is characterized by a complex system of sharp absorption-bands. The strongest ones are at 559, 973, 1361, 1445, 1520, 1574, 1652, 3145, 3452 and 3548 cm–1. The FTIR spectrum is very similar to that of dresserite and strontiodresserite (Farrell 1977). The slight shift in the absorption maxima is well explained by the effects of Ca replacement by Ba and Sr.
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X-RAY CRYSTALLOGRAPHY
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X-ray powder-diffraction scans of the mineral were recorded using a Philips model PW1050 Bragg–Brentano-type diffractometer with secondary monochromator with CuK radiation (
1.541862 Å). Synthetic fluorophlogopite (NIST SRM 675) was used as an internal standard. The data were indexed, and the resulting orthorhombic unit-cell was refined to a 15.564(6), b 5.591(4), c 9.112(4) Å, V 792.9(3) Å3. The axial proportions of the unit cell are a:b:c 2.7838:1:1.6298. Systematic absences indicate Pnma as the space group, in accordance with the other minerals of the dundasite group. The XRD scans reveal a strong tendency for preferred orientation, indicating that the needle-shaped crystals are elongate along the a axis. The X-ray powder-diffraction data for kochsándorite are given in Table 1.
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DISCUSSION
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Kochsándorite is the Ca-analogue of dresserite and a member of the dundasite group. The structure of dundasite was determined from single-crystal data (Cocco et al. 1972). Similarities in their FTIR spectra (Farrell 1977) and powder-diffraction data strongly suggest that dresserite (Jambor et al. 1969), strontiodresserite (Jambor et al. 1977) and kochsándorite are isostructural with dundasite. Kochsándorite is made up of geochemically common elements, and its formation did not require extreme conditions of temperature or pressure. The presence of böhmite nodules in coal presumably provided the unique environment that led to its formation in that mine.
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AKNOWLEDGEMENTS
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The first samples were collected by Lajos Kövecses-Varga, the owner of the Collection and Museum of Minerals of the Carpathian Basin in Siófok, Hungary. He placed the samples at our disposal. Further samples were collected and graciously provided by Csanád Lóránth of Budapest. We also thank Árpád Kovács (Department of Metallurgy, University of Miskolc) for SEM/EDS examinations and Ferenc Mádai (Department of Mineralogy and Petrology, University of Miskolc) for his help with the optical studies. We are indebted to Emma Jakab (CRC–HAS, Budapest) for the TG–MS measurements and Zsolt Révay for the PGAA results. We thank Ernst A.J. Burke, Joseph A. Mandarino, Robert F. Martin and the referees for their valuable comments, which improved the manuscript.
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REFERENCES
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BIRCH, W.D., KOLITSCH, U., WITZKE, T., NASDALA, L. & BOTTRILL, R.S. (2000): Petterdite, the Cr-dominant analogue of dundasite, a new mineral species from Dundas, Tasmania, Australia and Callenberg. Saxony, Germany. Can. Mineral. 38, 1467–1476.[Abstract/Free Full Text][CrossRef][ISI][GeoRef]COCCO, G., FANFANI, L., NUNZI, A. & ZANAZZI, P.F. (1972): The crystal structure of dundasite. Mineral. Mag. 38, 564–569.[CrossRef][ISI][GeoRef]
CSAJAGHY, G. & ZAMAROCZY, D. (1959): Pirites ásványkiválás a tatabányai szénmedencébõl [Pyrite mineral precipitation from the Tatabánya coalfield]. Földt. Közl. 89, 270–279. (in Hungarian).
FARRELL, D.M. (1977): Infrared investigation of basic double-carbonate hydrate minerals. Can. Mineral. 15, 408–413.[Abstract/Free Full Text][GeoRef]
GERBER, P. (1978): A Tatabánya – Nagyegyháza – Mány terület földtani-teleptani viszonyai [Geological characteristic of Tatabánya – Nagyegyháza – Mány area]. Földt. Közl. 108, 18–28 (in Hungarian).
JAMBOR, J.L., Fong, D.G. & Sabina, A.P. (1969): Dresserite, the new barium analogue of dundasite. Can. Mineral. 10, 84–89.[Abstract/Free Full Text][GeoRef]
JAMBOR, J.L., SABINA, A.P. & STURMAN, B.D. (1977): Strontiodresserite, a new Sr–Al carbonate from Montreal Island, Quebec. Can. Mineral. 15, 405–407.[Abstract/Free Full Text][GeoRef]
REVAY, ZS. & BELGYA, T. (2004): Principles of PGAA method. In Handbook of Prompt Gamma Activation Analysis with Neutron Beams (G.L. Molnár, ed.). Kluwer Academic Publishers, Dordrecht, The Netherlands (1–30).
REVAY, Zs., BELGYA, T., KASZTOVSZKY, ZS., WEIL, J.L. & MOLNAR, G.L. (2004): Cold neutron PGAA facility at Budapest. Nucl. Instrum. Phys. Methods B 213, 385–388.[CrossRef]
SZADECZKY-KARDOSS, E. (1952): Szénkõzettan [Coal Petrology]. Akadémiai Kiadó, Budapest, Hungary (in Hungarian).
VADASZ, E. (1941): Ásványkiválások a tatabányai eocén barnakõszénképzõdésben [Mineral precipitations in the Eocene brown coal deposit of Tatabánya]. Mat. Termtud. Értes. 60, 495–518 (in Hungarian).
Received May 31, 2006
,revised manuscript accepted September 19, 2006.
Copyright © 2008 by Mineralogical Association of Canada
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Abstract
Introduction
